Base station, base station module and method for direction of arrival estimation

ABSTRACT

The invention relates to a base station for a radio communications network. In order to be able to enhance the resolution for a direction of arrival estimation, the base station comprises: a first phasing network ( 31 ) for forming beams (B 1 -B 4 ) for fixed reception angles; a second phasing network ( 33 ) for co-phasing and summing the signals of at least two neighbouring beams (B 2 , B 3 ), thus forming a beam (B 2-3 ) for a reception angle in-between at least those two neighbouring beams (B 2 , B 3 ), and for scaling each resulting beam (B 2-3 ) with a predetermined factor; and means for estimating the direction of arrival in the uplink from the beams (B 1 -B 4 , B 2-3 ) provided by the first and the second phasing network ( 31, 33 ). The invention equally relates to a corresponding method and to a base station module comprising such a first and second phasing network.

FIELD OF THE INVENTION

[0001] The invention relates to a base station for a radiocommunications network, a module for such a base station and a methodfor enhancing the angular resolution in the estimation of the directionof arrival of signals in the uplink in a base station of a radiocommunications network.

BACKGROUND OF THE INVENTION

[0002] It is known from the state of the art to provide base stationswith smart antenna arrays which enable the output of fully steerabledownlink beams. When employed for a user specific digital beamforming, abeamformer of such a smart antenna array is e.g. able to weight phaseangle and/or amplitude of the transmitted signals in a way that thedirection of the beam is adapted to move along with a terminal throughthe whole sector of coverage of the antenna array.

[0003] In order to be able to move a downlink beam according to themovement of a terminal, the base station has to determine the directionin which the terminal can be found. This can be achieved by estimatingthe azimuth direction of arrival of the uplink signals received by thebase station from the respective terminal. For receiving uplink signals,base stations often employ a fixed beam reception system, the fixedbeams being evaluated for estimating the direction of arrival of theuplink signals.

[0004] For illustration, FIG. 1 shows an example of an architecture in abase station used for the processing of signals from a single user forestimating the direction of arrival (DoA).

[0005] The part of the base station depicted in FIG. 1 comprises anuplink digital beam matrix 11 connected at its inputs to a uniformlinear antenna array (ULA) with eight receiver antennas (not shown). Theoutput of the uplink digital beam matrix 11 is connected via means forstandard RAKE processing 12 to means for estimating the direction ofarrival of uplink signals 13. The means for estimating the direction ofarrival 13 are connected on the one hand to further components of thebase station that are not shown. On the other hand, they are connectedto processing means 14 suited for spreading and weighting of signals.The processing means 14 receive as further inputs signals from means fordownload bit processing 15 and output signals to means for user-specificdigital beamforming 16. The outputs of the means for user-specificdigital beamforming 16 are connected to eight transmit antennas (notshown). The means for standard RAKE 12, for estimation of the DoA 13,for downlink bit processing 15 and the processing means 14 are used fordigital base-band processing.

[0006] Signals entering the base station via the receive antennas arefirst processed in the digital beam matrix 11. The digital beam matrix11 is an M×M matrix, where M is the number of antenna elements, i.e. M=8in the described example. The digital beam matrix 11 generates from thereceived signals fixed reception beams in eight different directions.With the digital beam matrix 11 and the uniform linear antenna array(ULA), orthogonal beams (butler matrix) or an arbitrary set ofnon-orthogonal beams can be generated. The generated beams are input tothe means for standard RAKE 12.

[0007] After a processing on the chip level by the means for standardRAKE 12, the beams are evaluated in the means for estimation of thedirection of arrival 13 in order to be able to determine the bestdirection for transmission of downlink signals. The direction of arrivalof the uplink signals can be estimated by simply measuring the powerfrom each beam. In particular, the power in the pilot symbols in thechannel estimate can be determined. The beam direction of the beam withthe highest uplink power, averaged over fast fading, is considered asthe direction of arrival, to which the downlink beam is to be directed.Alternatively, the direction of arrival can be estimated with any otherknown method for determining the direction of arrival in the beam space.The means for estimation of the direction of arrival 13 provide theprocessing means 14 with power control and weight information forforming the downlink beams corresponding to the determined direction ofarrival.

[0008] In addition, further elements in the means for estimation of thedirection of arrival 13 forward soft bits, including the data signalstransmitted by the terminal, to the components not depicted in thefigure.

[0009] Hard bits constituting signals that are to be transmitted fromthe network to the terminal are processed, e.g. encoded, by the meansfor downlink bit processing 15 and forwarded to the processing means 14.The processing means 14 are able to spread and weight those signalsaccording to the information received from the means for estimation thedirection of arrival 13. The thus processed signals are transmitted tothe means for user-specific digital beamforming 16 which transmit thesignals via the transmit antennas in a downlink beam directed to thedetermined direction of arrival of the uplink signals.

[0010] With this method, the estimation of the uplink direction ofarrival is based on a rough resolution grid in the form of the fixedbeams. That means, even though in the downlink the transmission beam canbe steered continuously with arbitrary resolution, the accuracy of thedownlink beamforming is limited to the uplink beam spacing. Thisaccuracy is not adequate for downlink beam steering, if the number ofbeams is equal to the number of columns in the smart antenna array. Evenif the direction of arrival resolution is improved as the number ofreception beams is increased by increasing the number of receiveantennas, the angular resolution is not adequate with 4-8beams/antennas. In the uplink, the angular resolution is approximately30° with 4 beams and approximately 15° with 8 beams.

[0011]FIGS. 2a-d show this angular distribution of the fixed uplinkbeams for different constellations. FIG. 2a is a diagram with theamplitude beam pattern over the azimuth angle in degrees of fourorthogonal beams resulting from a 4-antenna array. FIG. 2b is a diagramwith the corresponding amplitude beam pattern of eight orthogonal beamsof a 8-antenna array. In contrast, FIG. 2c is a diagram with theamplitude beam pattern of four non-orthogonal beams of a 4-antenna arrayand FIG. 2d a diagram with the amplitude beam pattern of eightnon-orthogonal beams of a 8-antenna array.

[0012] Alternatively to basing the estimation of the direction ofarrival on the power of the fixed beams, the direction of the downlinkbeam can be selected by transforming the channel estimates back to theelement domain. To this end, the beamformed signals are multiplied by aninverted digital beam matrix to obtain the element space signals. Then,any known direction of arrival techniques is used in the element space.However, for practical implementations this method leads to an excessiveamount of computations.

SUMMARY OF THE INVENTION

[0013] It is an object of the invention to provide a base station, abase station module and a method which allow for a simple enhancement ofthe angular resolution in the estimation of the direction of arrival ofuplink signals.

[0014] This object is reached on the one hand with a base station for aradio communications network, comprising a first phasing network forforming beams for fixed reception angles out of signals provided by areceive antenna array and for outputting the signals constituting saidbeams; a second phasing network for co-phasing and summing the signalsprovided by the first phasing network for at least two neighbouringbeams, thus forming a beam for a reception angle in-between the at leasttwo neighbouring beams, and for scaling amplitude and/or power of eachresulting beam with a predetermined factor; and means for estimating thedirection of arrival in the uplink from the beams provided by the firstand the second phasing network.

[0015] On the other hand, the object is reached with a method forenhancing the angular resolution in the estimation of the direction ofarrival of signals in the uplink in a base station of a radiocommunications network, comprising:

[0016] receiving uplink signals with a receive antenna array of the basestation;

[0017] forming first beams for fixed angles of arrival out of thereceived signals in a first phasing network and outputting the signalsconstituting said beams;

[0018] forming at least one composite beam in-between at least twoneighbouring ones of the first beams in a second phasing network byco-phasing and summing the signals belonging to the neighbouring beamsand by scaling amplitude and/or power of each resulting composite beamwith a predetermined factor; and

[0019] estimating the direction of arrival of the received signals basedon the first beams and the composite beams.

[0020] The object is equally reached with a base station module for abase station comprising such a second phasing network.

[0021] The invention proceeds from the idea that a finer angularspectrum can be achieved by further processing the already beamformeduplink signals, which present a relatively rough angular spectrum. Thefiner resolution is achieved by simply applying multiplications andsummings on the present fixed beams, followed by a subsequent scaling. Amain advantage of the method, the base station and the base stationmodule according to the invention is therefore the simplicity with whicha finer angular resolution for the estimation of the direction ofarrival of uplink signals is achieved.

[0022] The estimated direction of arrival is used in particular forforming a downlink beam to be transmitted in said direction.

[0023] Preferred embodiments of the invention become apparent from thesubclaims.

[0024] A receive antenna array employed for receiving uplink signalsfrom a terminal and for providing the received signals to the firstphasing network of the base station can be comprised by the base stationof the invention or form an supplementary part of the base station. Thesame applies for a transmit antenna array.

[0025] The first phasing network can be suited for forming orthogonal ornon-orthogonal beams as fixed reception beams. Preferably, the firstphasing network is moreover suited to form four or eight of such beams,depending on the number of receive antennas from which it receivesuplink signals. However, any other number of receive antennas and to beformed beams can be chosen as well.

[0026] In an advantageous embodiment of the base station and the methodof the invention, co-phasing and summing of the signals of twoneighbouring beams provided by the first phasing network is carried outfor all neighbouring beams formed by the first phasing network.Accordingly, the total number of formed beams is twice minus one thenumber of the original beams formed by the first phasing network.Therefore, the resolution of the azimuth reception angle is doubled.

[0027] The power and/or the amplitude of the composite beams resultingfrom the co-phasing and summing should be scaled according to the powerand/or amplitude of the original beams, in order to make the compositebeams comparable to the first beams for determining the direction ofarrival. To this end, the composite beams can be scaled in a way thatequal gains are achieved for all beams. The scaling factors can also becan also be selected so that the signal-to-noise ratio (SNR) for eachbeam is equal in case that the same signal is arriving to each beam.Alternatively, the scaling factors can be selected so that thesignal-to-interference-and-noise ratio (SINR) for each beam is equal incase that the same signal is arriving to each beam.

[0028] In case the composite beams are formed exactly in the middle oftwo neighbouring orthogonal beams, with four original orthogonal beamsthe scaling factor can be set to a value which compensates the loss of0.67 dB for all composite beams and with eight original orthogonal beamsto a value which compensates the loss of 0.86 dB, in order to obtainequal gains for all beams. In the case of four orthogonal beams, inorder to compensate the loss of 0.67 dB, the power correction factor is16/13.7=1.1679, while the amplitude correction factor is 4/{squareroot}{square root over (13.7)}=1.0807.

[0029] For achieving an even finer tuning of the angular resolution withthe base station/base station module and by the method according to theinvention, the signals of neighbouring original beams are multiplied bydifferent predetermined factors before co-phasing and summing.Preferably, one factor is greater than 1 and the other factor smallerthan 1. This way, the composite beam or beams are not necessarily placedat an angle exactly in the middle of the two neighbouring beams but canbe shifted arbitrarily to any angle between the two original beams.

[0030] In this case, the scaling factor that has to be applied on theformed composite beams depends in addition on the factors used formultiplying the amplitudes.

[0031] The proposed fine tuning can be used in particular for generatingseveral beams at different angles in between two original neighbouringbeams by multiplying them with different sets of factors. Accordingly,any desired angular resolution can be obtained for estimating thedirection of arrival in the uplink.

[0032] The estimation of the direction of arrival in the uplink ispreferably based on an evaluation of the power of the beams provided bythe first and the second phasing network.

[0033] The first and the second phasing network can be analogue phasingnetworks, but preferably they are digital phasing networks in which acomplex valued weight vector represents each beam in the digital domain.Such digital phasing networks are advantageously formed by a digitalbeam matrix DBM.

[0034] In a digital phasing network, complex weights can be stored. Thecomplex weights are then applied to incoming signals for forming thedesired beams. The complex weights of the first digital phasing networkcan be predetermined in any suitable manner so they are suited to formthe predetermined number of beams at the predetermined angles. Thecomplex weights of the second digital phasing network are determined ina way that the beams provided by the first phasing network are co-phasedand summed in the second digital phasing network when applying thecomplex weights to the corresponding signals.

[0035] In the digital domain, the co-phasing of neighbouring beams canbe achieved by rotating the phase angle of at least one of the vectorsrepresenting two neighbouring beams. In the case of four orthogonaloriginal beams, the phase angle of the vector representing the first oftwo neighbouring beams can e.g. be rotated by 0 and the phase angle ofthe vector representing the second of the two neighbouring beams by+3π/4 or −3π/4, depending on which beam was selected as first and whichas second beam. In the case of signals received from an antenna arraywith eight antennas, formed into eight orthogonal beams, the phase angleof the vector representing the first of two neighbouring beams can e.g.be rotated by 0 and the phase angle of the vector representing thesecond beam by +7π/8 or −7π/8.

[0036] The rotated vectors of the two neighbouring beams are thensummed, thus forming a single vector. This single vector represents asingle composite beam in the middle of the two original neighbouringbeams.

[0037] Also the multiplication of different neighbouring beams withdifferent factors for fine tuning can be realised by multiplying theamplitudes of the corresponding vectors with different factors beforerotating and summing.

[0038] The method and the base station according to the invention canalso be used for estimating the angular spreading of signals impingingat the base station. For example, after finding the DOA with largestaverage power the corresponding power is measured also from bothadjacent beams. As described above, the increment of the direction anglefrom one beam to the adjacent beam can be set to be arbitrarily small.If the averaged power of the adjacent beam is above a pre-set thresholdthe number describing the angular spread is increased by the numbercorresponding to the angular increment between the two adjacent beams.The threshold can be also adaptive. For instance, the angular apertureof the entire sector is scanned and an average value for signal strengthis obtained which depends on the desired signal, the interferencescenario and the particular radio environment. The level of the desiredsignal is then compared to the averaged value describing the entiresector. If the desired signal exceeds the threshold the signal power ofthe next beam is then calculated. This process is repeated as long asthe power level of the desired signal is above the threshold. Thus theangular spread (AS) is directly proportional to the number of beams inwhich the averaged power of the desired signal is above the thresholdand to the angle interval between two adjacent beams:

AS=ND

[0039] where N equals the number of adjacent beams in which the desiredsignal power is above the threshold and D is the angle increment ofneighbouring beams. For example, in case of 8 original beams and 7mid-beams the angle increment D is approximately 7.5 degrees. If thesignal power exceeds the threshold in three consecutive beams theangular spread is 22.5 degrees assuming the same angle increment D frombeam to beam. It is also noted that the angle increment D may vary frombeam to beam which is the preferred case in orthogonal beams. If thesignal power exceeds the threshold in three consecutive beams theangular spread is 22.5 degrees.

[0040] The proposed base station, base station module and method areparticularly suited for an employment with WCDMA (wideband code divisionmultiplex access) and EDGE (enhanced data rate for GSM evolution; GSM:global standard for mobile communication).

BRIEF DESCRIPTION OF THE FIGURES

[0041] In the following, the invention is explained in more detail withreference to drawings, of which

[0042]FIG. 1 shows the architecture in a base station for the processingof uplink signals from a single terminal;

[0043]FIG. 2a shows orthogonal beams of a 4-antenna array;

[0044]FIG. 2b shows orthogonal beams of an 8-antenna array;

[0045]FIG. 2c shows non-orthogonal beams of a 4-antenna array;

[0046]FIG. 2d shows non-orthogonal beams of an 8-antenna array;

[0047]FIG. 3 shows components of a base station according to theinvention;

[0048]FIG. 4 illustrates the forming of complex weights in the firstdigital phasing network;

[0049]FIG. 5a shows a power beam pattern with one beam generatedaccording to the method of the invention;

[0050]FIG. 5b shows an amplitude beam pattern with three beams generatedand scaled according to the method of the invention for a 4-antennaarray;

[0051]FIG. 6a shows an amplitude beam pattern with seven beams generatedaccording to the method of the invention for an 8-antenna array;

[0052]FIG. 6b shows an amplitude beam pattern with seven beams generatedaccording to the method of the invention for an 8-antenna array withfine tuning;

[0053]FIG. 7a shows an exemplary power distribution over 8 originalbeams; and

[0054]FIG. 7b shows an exemplary power distribution over 8 original and7 composite beams generated according to the invention in between theoriginal beams.

DETAILED DESCRIPTION OF THE INVENTION

[0055]FIGS. 1 and 2a-d have already been described with reference to thebackground of the invention.

[0056]FIG. 3 depicts elements of a base station according to theinvention that are used in a method according to the invention.

[0057] In the base station of FIG. 3, a 4-antenna array is employed asreceive antenna array. Each antenna Ant1-Ant4 is connected via a lownoise amplifier LNA to a digital beam matrix DBM 31, which forms adigital phasing network and has stored complex weights. The digital beammatrix corresponds to the uplink digital beam matrix 11 in FIG. 1a,except that the digital beam matrix 31 of FIG. 3 is a 4×4 instead of a8×8 matrix. A calibration unit 32 has access to the low noise amplifiersLNA. The digital beam matrix 31 has an output line for each of fourbeams B₁ to B₄. The output lines for beams B₂ and B₃ are branched offand fed to a second digital phasing network 33. Also in the seconddigital phasing network 33 complex weights are stored. The seconddigital phasing network 33 has an output for a further beam B₂ _(—) ₃.

[0058] The antenna elements Ant1-Ant4 of the receive antenna arrayreceive uplink signals from a terminal, the signals entering the antennaarray from a certain direction depending on the present location of theterminal.

[0059] The signals received by the antennas Ant1-Ant4 are amplified inthe low noise amplifiers LNA, the low noise amplifiers LNA beingcalibrated by the calibrating means 32 in a way that the transmissionline from antenna elements Ant1-Ant4 to the digital beam matrix 31 canbe assumed to be identical.

[0060] In the digital beam matrix 31, four orthogonal fixed receptionbeams B₁-B₄ corresponding to those shown in FIG. 2a are formed byapplying the suitably selected and stored complex weights to thereceived signals. The power or the amplitude of each beam indicates thestrength of reception with a certain reception angle. The beams areoutput and fed to means for estimating the direction of arrival, asindicated e.g. in FIG. 1.

[0061] Two neighbouring beams B₂ and B₃ are fed in addition to thesecond digital phasing network 33. The second digital phasing network 33performs a co-phasing and subsequent summing of the two beams B₂, B₃ byapplying the further complex weights to the signals belonging to thebeams B₂, B₃. These complex weights are selected such that they cause aco-phasing and summing of the received beams received from the firstdigital phasing network 31. The result of the application of the complexweights is therefore a response in a direction in the middle between thedirections of the two original beams B₂, B₃. The amplitude and the powerof this composite beam B₂ _(—) ₃, however, is somewhat reduced comparedto the original beams B₂, B₃, when assuming the same signal strength inall three directions. When the amount of the reduction is known,however, the composite beams can be scaled so that the relative gain ofthe generated beam B₂ _(—) ₃, can be used in the means for estimatingthe direction of arrival for taking into account an additional azimuthangle.

[0062] It is now explained with reference to FIG. 4 how the scalingfactor can be obtained for orthogonal beams of the 4-antenna array usedin the base station of FIG. 3.

[0063] Co-phasing of two adjacent beams can be achieved by co-phasingthe complex valued weight vectors representing two neighbouring beams inthe digital beam matrix 31 in the digital domain. The vector b_(i) forbeam B_(i) is obtained by summing the elements a_(k) of thecorresponding array response vector a_(i):$b_{i} = {\sum\limits_{k = 1}^{N}\quad a_{k}}$

[0064]FIG. 4 illustrates in vector form how a digital beam matrix 31used for generating four orthogonal beams B₁-B₄ determines complexvalued weight vectors for beams B₂ and B₃. Given a 4-beam digital beammatrix, the elements of the corresponding vector are added for beam B₂,while the phase angle is rotated from one element to the next by 45°, asshown on the left hand side of FIG. 4. The resulting vector isb₂=1+2,414j. Similarly, the signals from the antenna elements are addedfor beam B₃, but here the phase angle is rotated from one element to thenext by −45°, as shown on the right hand side of FIG. 4. The resultingvector in this case is b₃=1−2,414j. Beam B₂ and beam B₃ are representedin the digital domain by these vectors b₂ and b₃.

[0065] The output of the first digital phasing network 31 can beco-phased by rotating the phase angle of beam B₂ or beam B₃ or both.Here, the phase angle of beam B₃ is rotated by 3π/4 to co-phase withbeam B₂. After co-phasing, the beams are summed, leading to a compositebeam B₂ _(—) ₃ represented by

b ₂ _(—) ₃ =b ₂ +b ₃=2+4.83j=5.23 exp (j3π/8).

[0066] While the power of the four beams B₁ to B₄ output by the digitalbeam matrix 31 is 16, the power of the resulting beam B₂ _(—) ₃ is0.5*(5.23)²=13.7. Thus, the loss compared to the original beam is13.7/16=0.67 dB. The knowledge of this loss enables a scaling of a beamgenerated in the middle of two fixed beams so that the relative gain ofthe generated beam is known and can be used for estimating the directionof arrival. The scaling factors are stored as well as the requiredcomplex weights.

[0067] For other kinds of digital beam matrices the scaling factors aredetermined analogously. With an 8-antenna array and a digital beammatrix forming 8 non-orthogonal beams B₁-B₈, for example, the outputsfor the two centre beams, B₄ and B₅, are b₄=1+5.03j and b₅=1−5.03j.After co-phasing the two beams B₄, B₅ by rotating B₅ by 7π/8, thecomposite beam B₄ _(—) ₅ is represented by

b ₄ _(—) ₅ =b ₄ +b ₅=2+10.05j=10.25 exp (j7π/16),

[0068] the power being 52.5 as compared to 64 for the original beamsB₁-B₈. Therefore, the loss in the antenna gain in this case is52.5/64=0.86 dB for an 8-beam digital beam matrix.

[0069] Instead of two adjacent beams, also more beams can be co-phasedand summed to obtain mid-beams.

[0070]FIG. 5a is a diagram of the power beam pattern obtained by thebase station of FIG. 3 without scaling in case of orthogonal Butlerbeams. The power is depicted over the azimuth angle from −100 to 100. Ascan be seen in the diagram, the power of the four original beams B₁ toB₄ is 16, while the power of the composite beam B₂ _(—) ₃ is 13.7, inline with the above calculation of the scaling factors.

[0071]FIG. 5b shows a diagram with the amplitude beam pattern of fouroriginal beams and three composite beams in case of non-orthogonalbeams, where the beams are roughly scaled with corresponding scalingfactors. The composite beams B₁ _(—) ₂, B₂ _(—) ₃, B₃ _(—) ₄ have beenformed between each existing pair of neighbouring original beams B₁/B₂,B₂/B₃ and B₃/B₄. It becomes apparent from this figure that the directionof arrival resolution can be doubled by introducing a composite beam inbetween all neighbouring original beams.

[0072] In another embodiment of the method according to the invention, afurther increase of the angular resolution can be obtained.

[0073] The above described embodiment applies only phase shifts to theoriginal beams, which provides one additional beam exactly between twoneighbouring beams. Providing such generated composite beams is notsufficient, if there is a need for fine tuning the directions of thecomposite beams.

[0074] In order to be able to achieve a finer resolution, complexweights causing phase shifts and amplitude adjustments to the receivedbeams are applied for neighbouring beams. This way, a composite beam canbe directed into any desired direction.

[0075]FIGS. 6a and 6 b illustrate the difference between beamforming byphase shifting only and beamforming by phase shifting and an additionaladjustment of the amplitudes of the original beams.

[0076]FIG. 6a is a diagram of the amplitude beam pattern from a 8-beamdigital beam matrix forming 8 orthogonal beams B_(i) (i=1 to 8). Theadditional composite beam pattern for seven composite beams B_(i) _(—)_(i+1) results from co-phasing and summing all neighbouring originalbeams B_(i) and B_(i+1) (i=1 to 7). Co-phasing was achieved by phaseshifting the phase φ_(i) of the first one of two neighbouring beamsB_(i) by Δφ_(i)=0 and the phase φ_(i+1) of the second one of twoneighbouring beams B_(i+1) by Δφ_(i+1)=−7π/8 for all pairs ofneighbouring beams. The composite beams have not been scaled, thereforethey appear in the figure with a lower amplitude than the originalbeams.

[0077] In FIG. 6b, in addition to the phase shifts of Δφ_(i)=0 andΔφ_(i+1)=−7π/8, the amplitude of the respective first neighbouring beamB_(i) was multiplied by 0.8 and the amplitude of the respective secondneighbouring beam B_(i+1) by 1.2 before summing. As a result, thegenerated composite beams B_(i) _(—) _(i+1) in FIG. 6b are shiftedsomewhat to the left as compared to the composite beams in FIG. 6a. Byvarying the factors with which the amplitudes of the original beams aremultiplied, the composite beams can thus be positioned at any anglebetween two original beams.

[0078] This approach enables in addition that several beams can beformed between every two neighbouring original beams simply by applyingdifferent sets of factors for the multiplication of the amplitudes ofthe original beams, which leads to an arbitrarily fine angularresolution.

[0079] Finally, FIGS. 7a and 7 b show the power distribution overdifferent non-orthogonal beams used in a base station by means forestimation of the direction of arrival of uplink signals. Bothdistributions correspond to the case that the signals from the terminalreach the receive antenna array of the base station perpendicularly,which is here to correspond to an azimuth angle of 0°. In FIG. 7a, thedirection of arrival is to be estimated from the power distribution over8 beams, all being formed by a first digital phasing network. Therelation between the different beams and the different angles of arrivalare the same as e.g. in FIG. 2d. In FIG. 7b, in contrast, the directionof arrival is to be estimated from the power distribution over 15 beams,including 7 composite beams formed in between the 8 original beamsaccording to the invention. As can be seen in FIG. 7a, beams number 4and number 5 have the maximum power. Accordingly, the means forestimating the direction of arrival are not able to determine the bestdirection for the downlink beam but only a best area which is lyingbetween the angles of beam number 4 and beam number 5. In FIG. 7b, themaximum power belongs clearly to beam number 8, positioned exactlybetween original beams 4 (here beam 7) and original beam 5 (here beam 9)and therefore at an angle of 0°. This shows that in the latter case, thebest direction for the downlink beam can be determined much moreaccurately.

1. Base station for a radio communications network, comprising: a firstphasing network (31) for forming beams (B₁-B₄) for fixed receptionangles out of signals provided by a receive antenna array and foroutputting the signals constituting said beams (B₁-B₄); a second phasingnetwork (33) for co-phasing and summing the signals provided by thefirst phasing network for at least two neighbouring beams (B₂, B₃), thusforming a beam (B₂ _(—) ₃) for a reception angle in-between the at leasttwo neighbouring beams (B₂,B₃), and for scaling amplitude and/or powerof each resulting beam (B₂ _(—) ₃) with a predetermined factor; andmeans for estimating the direction of arrival in the uplink from thebeams (B₁-B₄, B₂ _(—) ₃) provided by the first and the second phasingnetwork (31, 33).
 2. Base station according to claim 1, furthercomprising a receive antenna array for receiving signals from a terminaland for providing the received signals to the first phasing network (31)of the base station and a transmit antenna array for transmitting a beamin the estimated direction of arrival.
 3. Base station according toclaim 1 or 2, wherein the first phasing network (31) is designed to formorthogonal fixed reception beams.
 4. Base station according to claim 1or 2, wherein the first phasing network is designed to formnon-orthogonal fixed reception beams.
 5. Base station according to oneof claims 1 to 4, wherein the first phasing network (31) is designed toform four beams (B₁-B₄) out of the signals received from four receiveantennas.
 6. Base station according to one of claims 1 to 4, wherein thefirst phasing network is designed to form eight beams (B₁-B₈) out of thesignals received from eight receive antennas.
 7. Base station accordingto one of the preceding claims, wherein the second phasing network (33)is suited for scaling amplitude and/or power of the beams (B₂ _(—) ₃)formed in between two neighbouring beams (B₂, B₃) according to theamplitude and/or power of the beams (B₁-B₄) formed by the first phasingnetwork (31) in a way that the gain of all formed beams (B₁-B₄, B₂ _(—)₃) is equal.
 8. Base station according to one of the preceding claims,wherein the second phasing network (33) is suited for scaling amplitudeand/or power of the beams (B₂ _(—) ₃) formed in between two neighbouringbeams (B₂, B₃) according to the amplitude and/or power of the beams(B₁-B₄) formed by the first phasing network (31) in a way that thesignal-to-noise ratio for each formed beam (B₁-B₄, B₂ _(—) ₃) is equalin case that the same signal is arriving to each beam (B₁-B₄, B₂ _(—)₃).
 9. Base station according to one of the preceding claims, whereinthe second phasing network (33) is suited for scaling amplitude and/orpower of the beams (B₂ _(—) ₃) formed in between two neighbouring beams(B₂,B₃) according to the amplitude and/or power of the beams (B₁-B₄)formed by the first phasing network (31) in a way that thesignal-to-interference-and-noise ratio for each formed beam (B₁-B₄, B₂_(—) ₃) is equal in case that the same signal is arriving to each beam(B₁-B₄, B₂ _(—) ₃) .
 10. Base station according to one of the precedingclaims, wherein the second phasing network is suited for co-phasing andsumming the signals of all neighbouring beams (B₁-B₄) formed by thefirst phasing network.
 11. Base station according to one of thepreceding claims, wherein the second phasing network is suited formultiplying the signals provided by the first phasing network for twoneighbouring beams (B_(i), B_(i+1)) in between which a composite beam(B_(i) _(—) _(i+1)) is to be formed with at least one pair of differentpredetermined factors before co-phasing and summing in order to obtainat least one beam in-between the two neighbouring beams at at least onepredetermined azimuth angle.
 12. Base station according to one of thepreceding claims, wherein the means for estimating the direction ofarrival in the uplink are suited to evaluate the power of the beamsprovided by the first and the second phasing network for estimating thedirection of arrival.
 13. Base station according to one of the precedingclaims, wherein the first and the second phasing networks are analoguephasing networks.
 14. Base station according to one of the precedingclaims, wherein the first and the second phasing networks (31,33) aredigital phasing networks in which a complex valued weight vectorrepresents each beam (B₁-B₄) in the digital domain.
 15. Base stationaccording to claim 14, wherein in the first and the second digitalphasing network (31,33) complex weights are stored that are to beapplied to incoming signals for forming the respective beams.
 16. Basestation according to claim 14 or 15, wherein the second phasing network(33) is suited for co-phasing and summing at least two neighbouringbeams (B₂,B₃) by rotating the phase angle of at least one of the vectors(b₁,b₂) representing one of the two neighbouring beams (B₂,B₃) forobtaining two vectors with the same phase angle and by summing saidvectors (b₂,b₃) for obtaining a single vector (b₂ _(—) ₃) representing abeam (B₂ _(—) ₃) in between the two neighbouring beams (B₂,B₃).
 17. Basestation according to one of the preceding claims, further comprisingmeans for estimating the angular spreading of the received signals basedon the beams formed by the first and the second phasing network. 18.Base station module for a base station comprising a phasing network (33)according to the second phasing network of one of the preceding claims.19. Method for enhancing the angular resolution in the estimation of thedirection of arrival of signals in the uplink in a base station of aradio communications network, comprising: receiving uplink signals witha receive antenna array of the base station; forming first beams (B₁-B₄)for fixed angles of arrival out of the received signals in a firstphasing network (31) and outputting the signals constituting said beams(B₁-B₄); forming at least one composite beam (B₂ _(—) ₃) in-between atleast two neighbouring ones of the first beams (B₂,B₃) in a secondphasing network (33) by co-phasing and summing the signals belonging tothe neighbouring beams (B₂,B₃) and by scaling amplitude and/or power ofeach resulting composite beam with a predetermined factor; andestimating the direction of arrival of the received signals based on thefirst beams (B₁-B₄) and the composite beams (B₂ _(—) ₃).
 20. Methodaccording to claim 19, further comprising forming and outputting adownlink beam in the estimated direction of arrival of the uplinksignals.
 21. Method according to one of claims 19 to 20, whereinamplitude and/or power of the beams (B₂ _(—) ₃) formed in between twoneighbouring beams (B₂,B₃) are scaled according to the amplitude and/orpower of the beams formed by the first phasing network.
 22. Methodaccording to one of claims 19 to 21, wherein the factor for scaling isset to a value leading to an equal gain for each formed beam (B₁-B₄, B₂_(—) ₃) .
 23. Method according to claim 22, wherein the factor forscaling is set to a value which compensates the loss of 0.67 dB for allbeams (B₂ _(—) ₃) formed exactly in the middle of two neighbouring firstbeams (B₂,B₃) in case of a receive antenna array with four antennas andorthogonal first beams.
 24. Method according to claim 22, wherein thefactor for scaling is set to a value which compensates the loss of 0.86dB for all beams formed exactly in the middle of two neighbouring beamsin case of a receive antenna array with eight antennas and orthogonalfirst beams.
 25. Method according to one of claims 19 to 21, wherein thefactor for scaling is set to a value leading to an equal signal-to-noiseratio (SNR) for each formed beam.
 26. Method according to one of claims19 to 21, wherein the factor for scaling is set to a value leading to anequal signal-to-interference-and-noise ratio (SINR) for each formedbeam.
 27. Method according to one of claims 19 to 26, wherein the secondphasing network forms composite beams (B₁ _(—) ₂,B₂ _(—) ₃,B₃ _(—) ₄) inbetween each of the neighbouring first beams (B₁-B₄) formed by the firstphasing network.
 28. Method according to one of claims 19 to 27, furthercomprising multiplying the signals provided by the first phasing networkfor two neighbouring beams (B_(i),B_(i+1)) in between which a compositebeam (B_(i) _(—) _(i+1)) is to be formed with a different predeterminedfactor before co-phasing and summing in order to obtain a beamin-between the two neighbouring beams at a predetermined azimuth angle.29. Method according to one of claims 19 to 27, further comprisingmultiplying the signals provided by the first phasing network for twoneighbouring beams with different pairs of predetermined factors inorder to obtain differently weighted pairs of signals for each of theneighbouring beams, and subsequently co-phasing and summing each pair ofsignals in order to obtain a plurality of beams in between the twoneighbouring beams at predetermined azimuth angles.
 30. Method accordingto one of claims 19 to 29, wherein the beams are formed by analoguefirst and second phasing networks.
 31. Method according to one of claims19 to 29, wherein the beams are formed by digital first and secondphasing networks (31,33) in which a complex valued weight vectorrepresents each beams in the digital domain.
 32. Method according toclaim 31, wherein the first beams are formed by applying complex weightsto the received signals in the first digital phasing network (31), andwherein the co-phasing and summing of the signals of neighbouring beamsis carried out in the second digital phasing network (33) by applying tosaid signals of the formed beams for each to be formed composite beamfurther complex weights causing a phase angle rotation at least of oneof the vectors (b₂,b₃) representing the two neighbouring beams (B₂,B₃)for obtaining two vectors with the same phase angle and by summing saidvectors (b₂,b₃) .
 33. Method according to claim 32, wherein theco-phasing is carried out by rotating the phase angles of the vectors(b₂,b₃) of two neighbouring beams (B₂,B₃) by 0 and |3π/4| respectivelyin case of a receive antenna array with four antennas and orthogonalfirst beams.
 34. Method according to claim 32, wherein the co-phasing iscarried out by rotating the phase angles of the vectors of twoneighbouring beams by 0 and |7π/8|respectively in case of a receiveantenna array with eight antennas and orthogonal first beams.
 35. Methodaccording to one of claims 19 to 34, further comprising estimating theangular spreading of the received signals base on the formed first andcomposite beams.